1. Field of the Invention
The present invention relates to a process for producing an alkenyl substituted aromatic compound having one or more hydroxyl or amino groups in the aromatic ring thereof from the catalytic dehydrogenation of an alkyl substituted aromatic compound. The resultant alkenyl substituted aromatic compounds are suitable for use as the starting materials for the production of, for example, agricultural chemicals (or pesticides), resin modifiers for epoxy resins, polyamide resins, polycarbonate resins and the like, and comonomers for various polymers.
2. Description of the Related Art
Various processes for producing alkenyl substituted aromatic compounds having a hydroxyl or amino group in the ring thereof are known in the art. For example, alkenyl substituted aromatic compounds having an amino group in the ring thereof, i.e., alkenyl substituted anilines, can be produced by cleaving hydroxyphenyl-aminophenyl-alkanes in the presence of a basic catalyst (see Japanese Examined Patent Publication (Kokoku) No. 41-1937). Alternatively, Annalen der Chemie 472, 11 (1929) discloses the production of alkenyl substituted anilines from the equi-molar reaction products of carbonyl compounds and aromatic amines. However, the yields of these methods are not good and it has not been proposed that alkenyl substituted anilines are obtained from a catalytic dehydrogenation of alkyl substituted anilines.
On the other hand, alkenyl substituted aromatic compounds having a hydroxyl group in the ring thereof, i.e., alkenyl substituted phenols, can be produced by dehydrating 2-hydroxy-2-propyl phenols in the presence of an acidic catalyst (see Journal of Organic Chemistry Vol. 23, 544 (1958)), but the yield of this method is not good. Alternatively, several methods have been proposed to produce alkenyl substituted phenols from the catalytic dehydrogenation of alkyl substituted phenols. For example, Japanese Examined Patent Publication (Kokoku) No. 53-43491 discloses the use of dehydrogenation catalysts composed of, as a main active component, an iron oxide or a combination thereof with an oxide of alkaline earth metal. However, this method involves problems in that the conversion of the starting material and the yield of the desired product are low. Japanese Unexamined Patent Publication (Kokai) Nos. 54-55529 and 55-154930 disclose the use of a dehydrogenation catalyst composed mainly of a chromium oxide. However, these methods involve problems in that the conversion of the starting materials is less than 40% and the yield of the desired product is also low. More particularly, the catalysts disclosed in Japanese Patent Kokai No. 54-55529 are composed of chromium oxides alone or a combination thereof with oxides of zinc, manganese, titanium, and/or zirconium. The activities of these catalysts are, however, low because the yields of the desired products are less than 40%. In addition, although this patent publication discloses, as a comparative example, the dehydrogenation of p-ethyl phenol with a commercially available catalyst composed of iron oxide, chromium oxide, and potassium oxide, the conversion and the selectivity of the desired product are even lower (i.e., conversion=11.5%, selectivity of p-ethenyl phenol=29.4%). The present inventors obtained a similar result from the dehydrogenation of alkyl phenols using a commercially available catalyst having the same components (i.e., a Nissan Girdler catalyst G64A composed of Fe.sub.2 O.sub.3 (73.5%), Cr.sub.2 O.sub.3 (1.9%), and K.sub.2 CO.sub.3 (21.6%)) corresponding to the above-mentioned known catalyst, although the composition ratio of the metal oxides thereof is not clear. Thus, this type of catalyst cannot be practically used in the production of alkyl substituted phenols. The catalysts disclosed in Japanese Patent Kokai No. 55-154930 are composed of, as a main component, chromium oxide combined with metal oxides such as oxides of tin and iron. Although there are no specific disclosures as to the composition ratio of the catalyst in this specification, the chromium oxide-iron oxide catalyst used in Example 2 thereof is composed of about 50 parts by weight of the iron oxide based on 100 parts by weight of the chromium oxide. Such a catalyst containing, as a main component, the chromium oxide has a low activity and, therefore, is not suitable for use in the production of alkenyl substituted phenols from the practical point of view.
Furthermore, Japanese Unexamined Patent Publication No. 58-49328 discloses the production of ethenyl phenol from ethyl phenol using the oxides of barium and tin. This method, however, involves problems in that the conversion of the starting ethyl phenol and the yield of the desired ethenyl phenol are low.
However, as is well-known in the art, it is possible to change the catalyst activities when the composition ratio is varied, even when the constituents are the same. That is, it is possible to find a new catalyst having a higher activity compared to conventional catalysts by studying and appropriately modifying the known catalysts.